SPI and I2C, was Re: Raspberry Pi and America,

On Jul 1, 2012, at 3:42 PM, Tony Duell wrote: I'm late to this discussion because I've been out of town, but I thought I'd at least throw my two cents in. I don't understand why anyone would consider either I2C or SPI "superior" to the other. They have distinct advantages in certain situations, and distinct disadvantages in others. In my line of work (and I use both extensively), I2C is used for low-bandwidth communications with minimal pin count, and SPI is used for high-bandwidth or low-complexity communications when you can sacrifice a few pins. The fact that SPI can be implemented with basically just a few shift registers (or even just one, if it's write-only) gives it a huge advantage over I2C when resources are constrained; it's a lot easier to build an SPI interface out of 74xx parts than it is to build an I2C one. They also take up a lot less space on an FPGA. :-) For the wireless sensor mote system I designed (which is really just a backplane-based computer platform in miniature), I2C is used primarily for maintenance communication between the processors on the stack, while SPI is used for most data traffic (radio, most sensors, etc). The design of the system reflects the constraints the bus gives you; you can have a theoretical maximum of 127 boards in a system, but you can only have 4 SPI chip selects, so not all boards use the SPI (nor do they need to). - Dave